Circuit Breaker Modernization and Faster Fault Clearing on Single-Phase Electrified Railroad

The circuit breakers designed in 1913 for sectionalizing the 11/22 kv 3-wire trolley and feeder circuits on the New Haven Railroad electrification had become inadequate by 1936 because of limited interrupting capacity to clear line faults fast enough to insure system stability and reliability. Although these were never designed to handle the entire fault interrupting duty, space and weight limitations in the switching stations and supporting structures ruled out their replacement with modern circuit breakers of conventional design adequate for faster fault clearing. The application of modern interrupters to the original circuit breakers, together with the redesign of tanks, operating mechanism and supporting frames (with spring supports), produced a circuit breaker of approximately the same over-all dimensions and weight which by high-power laboratory tests proved to be adequate to interrupt the entire fault current (instantaneous rms symmetrical) as determined by a-c network calculator studies of the system. These studies were also the basis of application of instantaneous overcurrent relays for fault clearing by the line circuit breakers, of which there are over 500, making this system one of the largest installations with this type of relay protection. An analysis of the network calculator studies, the tests of the redesigned circuit breaker, and the operating results with their application are here reported.